Process for electrolytically depositing metallic material



R. F. CREW I 08,920 I PROCESS FOR ELEcTRoLYTIcAL Y DEPOS'ITING METALLIC MATERIAL Sept. 28, 1965 Filed Aug. 9, 1962 ac: sou/eat: i

7 A65 Attorney 3,208,920 PROCESS FOR ELE'CTROLYTICALLY DEPOSIT- ING METALLIC MATERIAL Richard F. Crew, Alma, Mich., assignor to General Electric Company, a corporation of New York Filed Aug. 9, 1962, Ser. No. 215,849 4 Claims. (Cl. 204-10) This invention relates to'an improved process for the preparation of metallic material by the electrolytic deposition of the metallic material into a liquid metal cathode.

Magnetic materials comprising elongated, single domain particles of improved magnetic properties may be obtained by the electrolytic deposition f fine metal magnetic particles into a pool of a liquid metal cathode, usually mercury. Such magnetic materials and their process of preparation are disclosed in US. Patent 2,974,104,

which issued on March 7, 1961, and is assigned to the same assignee as the present invention.

During such electrodeposition, undesirable plating of the fine particles may occur on the tray on which the mercury is retained and on other portions of the cathode assembly. This interrupts and shortens the deposition cycle, requiring frequent removal of the components of the cathodeassembly for cleaning and decreases the usable life span of such component's.

Various methods'for avoiding such .platingon the cathode assemblycomponents have proved unsuccessful. Decrease of current density, shortening of the plating cycle, use of special detergents in the electrolyte or the coating of the trays or other components of the cathode assembly with various non-conductivqorganic materials either does not avoid the undesirable. plating or results in degradation of 'the magnetic properties of the particles.

Ithas now been found that the foregoing and other" objects of thisinvention may be achieved bycoatinglthe surfaces of the liquid metal ."ca-thode assembly with a polysiloxane fluid.v The polysiloxane fluid does notatfect the conductivity 'of-the anode,'cathode-or electrolyte nor does it adversely affect the quality of the plated material.

United States Patent 3,208,920 Patented Sept. 2s, 1965 sist of the soluble salts of the ferromagnetic metals in the form of, for example,,sulfates or chlorides. The pH of the electrolyte is made acidic with, for example, sulfuric or hydrochloric acid, a preferred pH being a'b'out'2. A consumable anode is used of either the pure ferromagnetic metal or alloys of several ferromagnetic metals. .A nonconsumable anode of an-inert material, suchvas graphite, may also berused. A current density between 5 and 100 amps/sq. ft. may be used. The electrolyte may 'be at room temperature of 20 to 30 C, -duringelectrodeposi-' tion, although other electrolyte temperatures may be used if suitable adjustments are made incurrent density and time of deposition.'- The foregoing process is more fully disclosed in the above-identified US. Patent 2,974,104 and in copendingapplication S.N. 161,033, filed December 21, 1961, and assigned to the same assignee as the present invention. v

The drawing,'illustrating an electrodepos'ition apparzv tus for carrying out the above process, shows an electro-" plating cell 1,.including a glass tank 2, two vertically-suse pended, consumable iron anodes 3, an electrolyte 4 con- The polysiloxane. coating sufliciently inhibits plating on the cathode assembly components topermit an increase of over twofold in thelength'of time for a given plating cycle and results-in substantially reduced labor time'in- 'volved in removing-cleaning and replacing the cathode assembly components. The invention is particularly use-' 'ful in the preparation of elongated single domain magnetic particles prepared in accordance with the teachings,

of the a'bove-'mentioned US. Patent 2,974,104.

The term cathode'container assembly as used herein means electrically insulated components of the electrolytic apparatus either in contact with, or in close proximity to,. the liquid metal cathode.-

include thetray or other retaining surface for the cathode,

the cathode, such as devices for feeding the liquid cathode into the tray. All of these components are either composed entirely of, or coated with, organic or inorganic electrically insulating materials-such as glass, polyvinyl chloride, polyethylene, polystyrene, polyesters or other non-conductive materials well known in the art.

The invention will be more clearly-understood by reference to the following description taken in connection Such components ordinarily coatonly those sisting of an aqueous solution of ferrous sulfate, and a tray 5 in which is containedthemercury cathode 6. The tray 5 is suspended in the electrolyte from insulated suspension rods'7 connected to a cross supportS resting on tank 2. Anode lead 9 and cathode lead 10 are connected to the positive and negative terminals, respectively, of a suitable D.C."source. v i

In accordancewith the practice of this invention, the tray 5, the suspension rods 7 andthe lead 10 are coated with a-po'lysiloxane fluid before electrodeposition is begun. It ispreferable to coat all surfaces of the cathode assembly within the tank '2 withthe polysiloxane fiuid'a-lthough it has been found'that undesirable plating occurs largely on thoseisurfacesin closest proximity to the surface of the liquid metal cathode. It may therefore be suflicient to portions of the cathode assembly on which such plating occurs. I The polysiloxane fluids which are useful inthe practice ofthe present invention are liquid organopolysiloxane linear 'orbranch chain-compounds of the type disclosed in .5. Patent 2,469,888 which issued-on May 10, "1949 As the re described,

these organopolysiloxane chain com- 'poundshave'the general formula I (2a+.2 a (a-1) in -which the various Rs; represent the same or different lowermonovalenthydrocarbon radicals selected from the [class consisting of lower alkyl', aryl, valkaryl, and aralkyl radicals, examples ofwhich are the methyl, ethyl, propyl,

phenyl, benzyl, tolyl and xylylradicals and a is a whole structural members for supportingor suspendingthe tray, cathode leads and-other components in association'with' number equal to at least 3.

A preferred class of polysiloxane fluids are: the trimethyl silyl chain-stopped methyl polysiloxane's fthe formula where n is a positive integer. I

The invention is illustrated by the following examples.

H Example 1 This example illustrates a deposition process for elon gated, single domain iron particles using normal deposition current.

Iron particles were deposited using an electrolyte of 1 other.electrodeposi tion methods to preventundesirable plating on the cathode assembly. W

ferrous sulfate of 1.52 molarity, two vertically-suspended iron anodes and a mercury cathode retained on a plastic tray of polyvinyl chloride, Portions of the tray, of the suspension rods and of the cathode-lead adjacent to the mercury cathode, werecoated with a trimethyl silyl chainstopped dimethylpolys'iloxanehaving a viscosity of 350 centistokes at.25 -C. Other portions of the cathode assemincludes acathode container-assembly of electrically 'insu'lating' material for suppor'ting said liquidmet'a'l cathode said cathode container;a's-sernbly being coated with a polybly components adjacent to the mercilry were left'lill'r coated? The pH of the electrolyte was"2.0.- Ele'ctro-ldeposition proceeded at'a current densityot 25 amps/sq.

of 1 hour. The electrolyte was at room te'm-" ft. for a time perature.

At the conclusion of the electroplating cy"cle,}. thecoated portions ofthe tray','cathode lead and cathode suspension rods, were observed to be freeof undesirable deposition. 7 a The'uncoated surfaces of the cathode assembly contained undesirable electroplated material. Example 2 The electrodeposition process,-of' E xampl'e 1 was rejpeated exceptthat thecu'rrent density was increased to 219 vamps/sq. ft almost'nine times the. curr'ent'den'sity normally used for electrod eposition of fine magnetic par tic'les. For the-duration 'of the electrodeposition cycle, the 'po'lysiloxa'nel covered surfaces were free of deposited particles, "whereas uncoated cathode assembly surfacesr became platedt'.

Tests were ,made to determine theeffect of the poly-i siloxane coating on'themagnetic'quality of the-clepo sit ed.l particles. No degradation of properties was'pbserved Moreover, platingcycles-the. duration for which the cell (I assemblyrmay be continuously used without: eleaning" v were extended'approximatelytwo and onehalf times with aconsidera'ble reduction in man-hours spent for inspecji tion and cleanin'gof the cell assemblies.

The ',magnetic particles which may be deposited cordan'cewith the preferred embodiment of the invention may be anyferromagnetic metal or alloysuch as;'-'for-e'xample,.iroi1,v nickel, .co'baltor alloys of iron, nickel and cobalt with each other or with other metals; While the I 7. in acinvention has. .beenparticularly described 'in' connection with "the" electrodeposi'ti'on of' elongated, "single domain magnetic particles, itimay' be used in connection with a 2'."- A. prt cessgcdniprising electrolytically depositing-fine particle"fe'rr'oma'gnetic material from an electrolyte comprising metallic:'ionstif t he' j ferrorna'gnetic material into a 'me'rcury cath de: 'saidprocess 'bc'ing carried' outfin an electrolytic cell"which-includes a cathode container assem- 'blyof electrically insulating material for supporting said liquid metal cathodeflsaid cathode container assembly beingicoatedwith apolysiloxane fltiid.=

3. The "processot claim 2 in which -'said polysil 'oxant fluid i's a 'trir'nethylj s'ilyl,chain-stoppedimethyl polysi-loaan'e a A processflcomprising electrolytically depositing fine Particle ferromagnetic material selected from the grou;

consisting of iron, cobalt and nickel, and alloys of iron cobalt'a'ndmickel;from'anelectrolyte comprising' metallit -'ions ,'of the. magnetic -1iiateria'l- -into; 'a mercuryi cathodt -whilemaintaining{aguiescentinterface' between the cath ode and"electrolytefisaid}; process -.bein'gcarried' out in at elefct rolyti'c .cel l which'inclu'des a'cathode container assem bly "or electrically insulating material for supporting saic j liquidlJmeta-l"cathod9,"said. cathode-I container assembly being coated with'apolys'iloxane fluid.

fI Rte'tjeren'ceis Qitedby the I l 'UNi r'EosrnTEs PATENTS" JbrlN -H."MACK,"Pr q y mm 

1. A PROCESS COMPRISING ELECTROLYTICALLY DEPOSITING METALLIC MATERIAL FROM AN ELECTROLYTE COMPRISING METALLIC IONS OF THE MATERIAL INTO A LIQUID METAL CATHODE, SAID PROCESS BEING CARRIED OUT IN AN ELECTROLYTIC CELL WHICH INCLUDES A CATHODE CONTAINER ASSEMBLY OF ELECTRICALLY INSULATING MATERIAL FOR SUPPORTING SAID LIQUID METAL CATHODE, SAID CATHODE CONTAINER ASSEMBLY BEING COATED WITH A POLYSILOXANE FLUID. 